Hydrocarbons may be recovered from hydrocarbon-bearing formations by penetrating the formation with one or more wells through which the hydrocarbons may flow to the surface. Conditions (e.g., permeability, hydrocarbon concentration, porosity, temperature, pressure, water production rates, amongst others) of the formation may affect the economic viability of hydrocarbon production from the hydrocarbon-bearing formation. A hydrocarbon-bearing formation may have natural energy (e.g., gas, water) to aid in mobilizing hydrocarbons to the surface of the hydrocarbon-bearing formation. Natural energy may be in the form of water. Water may exert pressure to mobilize hydrocarbons to one or more production wells. Gas may be present in the hydrocarbon-bearing formation (reservoir) at sufficient pressures to mobilize hydrocarbons to one or more production wells. The natural energy source may become depleted over time.
Supplemental recovery processes may be used to continue recovery of hydrocarbons from the hydrocarbon containing formation. Examples of supplemental processes include waterflooding, polymer flooding, alkali flooding, thermal processes, solution flooding or combinations thereof.
In chemical enhanced oil recovery (EOR) the mobilization of residual oil saturation is achieved through surfactants which generate a sufficiently (ultra) low crude oil/water interfacial tension (IFT) to give a capillary number large enough to overcome capillary forces and allow the oil to flow (I. Chatzis and N. R. Morrows, “Correlation of capillary number relationship for sandstone”. SPE Journal, Vol 29, pp 555-562, 1989). However, reservoirs have different characteristics (crude oil type and composition, temperature and the water composition—salinity, cation distribution, hardness) and it is desirable that the structures of added surfactant(s) be matched to these conditions to achieve a low IFT. In addition, a promising surfactant must fulfill other important criteria including low rock retention, compatibility with polymer, thermal and hydrolytic stability and acceptable cost.
Compositions and methods for enhanced hydrocarbon recovery utilizing an alpha olefin sulfate-containing surfactant component are known. U.S. Pat. Nos. 4,488,976 and 4,537,253 describe enhanced oil or recovery compositions containing such chemicals. Compositions and methods for enhanced hydrocarbons recovery utilizing internal olefin sulfonates are also known. Such a surfactant composition is described in U.S. Pat. No. 4,597,879. The compositions described in the foregoing patents have the disadvantages that brine solubility and divalent ion tolerance are insufficient at certain reservoir conditions, which render the products unsuitable for said hydrocarbon-bearing formations.
U.S. Pat. No. 4,979,564 describes the use of internal olefin sulfonates in a method for enhanced oil recovery using low tension viscous waterflood. An example of a commercially available material described as being useful was ENORDET Internal Olefin Sulfonate, IOS 1720, a product of Shell Oil Company identified as a sulfonated C17-20 internal olefin sodium salt. This material has a low degree of branching. U.S. Pat. No. 5,068,043 describes a petroleum acid soap-containing surfactant system for waterflooding wherein a cosurfactant comprising a C17-20 or a C20-24 internal olefin sulfonate was used. In “Field Test of Cosurfactant-enhanced Alkaline Flooding” by Falls et al., Society of Petroleum Engineers Reservoir Engineering, 1994, the authors describe the use of a C17-20 or a C20-24 internal olefin sulfonate in a waterflooding composition with an alcohol alkoxylate surfactant to keep the composition as a single phase at ambient temperature without significantly affecting performance at reservoir temperature. In the above-mentioned reference, the reservoir water had a salinity of about 0.4 wt % sodium chloride. There is also industry experience with the use of certain alcohol alkoxysulfate surfactants. These materials, used individually, also have disadvantages under very severe conditions of salinity, hardness and temperature, in part because certain alcohol alkoxysulfate surfactants are not stable at high temperature, i.e., above about 70° C.
A crude oil (including any generic low API heavy crude oils and/or high API light crude oils) may contain significant amounts of specific solubility groups and chemical families. The overall distribution of both solubility groups and chemical families is a direct result of geochemical processes. The recovery of crude oil containing such components using surfactant flooding presents some unique problems. Such specific solubility groups include saturates, aromatics, asphaltenes and resins. Some of these solubility groups are natural surfactants present in the crude oil. These are polar fractions which under particular conditions may be surface-active and may adversely affect crude oil phase behavior during production operations. Moreover, solubility groups may also contain paraffins, naphthenic acids and basic components. Some of these specific chemical families are known to contribute towards emulsion stabilization under production conditions of oilfield fluids. For naphthenic acids, surface-activity is also a function of pH value. Naphthenic acids and their particular phase behavior may therefore interfere with the desired performance of a surfactant EOR chemical. Crude oils are normally classified using API gravity but this number may mask many of the more detailed characteristics of fluid phase behavior. An understanding of phase behavior, and thus more detailed prediction of chemical EOR may only be achieved by investigating crude oil compositions in more detail (e.g. solubility groups as well as specific chemical families). It appears that conventional surfactants do not provide the desired benefits for certain crude oils. For instance, even internal olefin sulfonates containing up to 20-24 carbons are not sufficiently effective for this commercial use. This may be due to competing solubilization effects of the many components of crude oils in hydrocarbon-bearing formations.